Valid 270100Z – 271200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER/MID MS VALLEY…
Isolated severe storms, with a threat for damaging winds and a few
tornadoes, will remain possible across parts of the lower to mid
Mississippi Valley and Midwest tonight.
…Lower Mississippi Valley to the Mid-South…
Widespread cloudiness and precipitation hampered diurnal heating and
related destabilization earlier today for much of the warm sector
across the lower MS Valley into the Mid-South. Still, slightly
greater instability exists this evening over southern AR into
northern LA, where surface dewpoints have risen into the mid to
upper 60s. Strong shear remains present across this region as an
upper trough over the Plains ejects northeastward. Convection that
formed earlier this afternoon and which remains ongoing this evening
has shown occasional low-level rotation. An isolated tornado and
damaging wind threat should continue through tonight as storms move
northeastward given that strong shear will persist. But, the lack of
greater instability owing mainly to poor mid-level lapse rates will
likely limit a more widespread damaging wind risk into the
Mid-South. Additional storms may form late tonight into early
Wednesday morning along an eastward-surging cold front/dryline, but
low-level winds will be slowly veering with time.
…Mid Mississippi Valley to the Midwest…
A powerful mid-latitude cyclone with 100 kt mid-level jet will move
northeastward across the mid MS Valley into the Midwest and Great
Lakes region by the end of the period. Storms have recently
developed along a composite cold front/dryline across southwestern
MO and near the OK/AR border. Very strong effective shear (50-60
kt) is being estimated by latest mesoanalysis across this region.
However, low-level moisture becomes considerably more limited with
northward extent from northern AR into MO. Current expectations are
for a broken line of storms to move quickly northeastward across MO
this evening, posing both a damaging wind and isolated tornado
threat. As these storms encounter a less unstable airmass with
eastward extent into IL/IN overnight, they should gradually weaken.
But, a marginal/gusty wind risk may continue through early Wednesday
morning across these areas given the very strong flow aloft.